The poxvirus molluscum contagiosum (MCV) causes benign papules in healthy people but disfiguring skin lesions in immunocompromised patients. No effective treatment for MCV infection is presently available. MCV appears to be a good candidate for chemotherapy, because antiviral agents might be applied topically rather than systemically, thereby reducing possible toxic side effects. Bushman and colleagues proposes to carry out mechanistic and pharmacological studies of the topoisomerase enzyme encoded by MCV. Studies of poxviruses have revealed that the virus-encoded topoisomerase is required for replication, indicating that inhibitors of this enzyme are likely to obstruct viral growth. A DNA encoding MCV topoisomerase has been cloned and overexpressed, and assays have been established for activity in vitro. Mechanistic studies have centered on understanding DNA-protein contacts important for function and the domain structure of the enzyme. Pharmacological studies have yielded an initial panel of enzyme inhibitors. The PI proposes to carry out extensive studies of the enzyme function, structure, and pharmacology. They will investigate the mechanism of topoisomerase function in vitro, the domain organization of the enzyme, and the structure of domains and the full-length enzyme. They will investigate the function of the enzyme in vivo, and use the assays developed to characterize inhibitors. An extensive compound screening program will be carried out to identify inhibitory small molecules. It is postulated that the combination of screening and thorough mechanistic and structural studies offers the most promising long-term route to inhibitor development. In addition, poxviruses have been implicated as possible biological warfare agents; thus poxvirus topoisomerase inhibitors might be use for treating such infections.